Professor Yong Luo’s research group reconstructed the Arctic temperature dataset of last hundred years, revealing a continual global warming trend

Professor Yong Luo’s research group reconstructed the Arctic temperature dataset of last hundred years, revealing a continual global warming trend

On November 20th, a group of researchers under the dynamic leadership of Prof. Yong Luo (Department of Earth System Science, Tsinghua University) and in collaboration with Prof. Xiangdong Zhang (University of Alaska, Fairbanks), Dr. Suping Nie (Associate Research Fellow in the National Climate Center), and others, published an online article entitled “Recently amplified arctic warming has contributed to a continual global warming trend” in the journal Nature Climate Change. Using a new interpolation method, a set of surface temperature sequences in the Arctic region over a time span of more than 100 years with a strong spatial and temporal homogeneity was established. Analysis of the new dataset shows that the global climate is persistently warming without any sign of hiatus or slowdown. New insights have been put forward to the international scientific community to debate over the existence of a “global warming hiatus” and its possible mechanism in recent years.

From the beginning of 2009, the topic of a “global warming hiatus” has puzzled the entire scientific community. Researchers have put forward different views to explain the mechanism and have also regarded it as a new challenge to global warming research. The term “global warming hiatus” refers to the slowdown or pause in the global mean temperature rise around 1998, although the emission of carbon dioxide and other greenhouse gases are still on the rise. The temperature increased by 0.05℃ per decade in 1998–2012, which was much lower than the average warming rate of 0.12℃ per decade since 1951.

Linear trends and associated uncertainties in the global mean annual SAT data based on reconstructed Arctic temperatures during the eight time periods of our interest are shown in the figure. In the inset, the results of the latter five periods are zoomed in. The results from the annual mean temperature change rate of NOAA for reconstruction (filled black triangles), the monthly mean temperature change rate of the original NOAA (filled blue circles) and the global mean temperature change rate after the Arctic temperature reconstructed in this paper (filled red squares) are shown here. Color bars denote a 90% confidence interval. (Unit: ℃/10 years)

The inconsistency between the manifestations of a “global warming hiatus” and the continuous increase of CO2 concentrations in the atmosphere puzzled the researchers, who doubt whether global warming has stalled. Are anthropogenic greenhouse gas emissions key to global warming? Is there any need to step up efforts to reduce greenhouse gas emissions? To answer these major scientific issues of widespread concern, climatologists around the world have conducted extensive research from the perspectives of, e.g., the effects of solar activity, volcanic activity and other external forces, deep oceanic heat content, and the role of the Pacific Ocean and the North Atlantic Ocean.

However, surface temperature observation sites are unevenly distributed globally, especially in the Antarctic and the Arctic regions where the observations are extremely sparse. Therefore, to what extent is the influence on the judgment of a “global warming hiatus” when calculating the global mean temperature in the absence of the Arctic region, which has been rapidly and intensively warmed in recent years? This is the pressing scientific problem that needs to be solved urgently.

The team has used the latest global temperature observation dataset released by the National Oceanic and Atmospheric Administration (NOAA) (lack of observation data in the polar region), and the Arctic temperature buoy dataset released by the International Arctic Buoy Programme (IABP) from 1850 to 2014 and from 1979 to 2004 respectively for their analysis. They applied the Data Interpolating Empirical Orthogonal Functions (DINEOF) method, which takes full advantage of the temporal and spatial coordination of the Arctic temperature, to reconstruct the temperature dataset in the regions with sparse observations, finally establishing a set of annual mean temperature series covering an area north of 50 oN, and from 1900 to 2014.

Research based on the new dataset found that the Arctic region has experienced accelerated warming after 2000. The global mean temperature including the Arctic region shows a warming trend of 0.112℃ per decade in 1998–2012, which is significantly higher than the trend that excludes the Arctic region (0.05℃ per decade). The result is surprisingly similar to the warming trend in 1951–2012. This study reveals for the first time that rapid Arctic warming may offset the cooling effects in the tropical eastern equatorial region on the global mean temperature in recent years. Although the spatial pattern of global warming has changed, the increasing trend in the global mean temperature has not changed. The study further points out that the lack of observation data in the Arctic region has a far greater impact on the calculation of the global mean temperature than that in the Antarctic region. The conclusion of the study clarifies the current debate over the “global warming hiatus”, namely, that global warming is still continuing without a hiatus or slowdown.

From left to right: Qiyi Zhang, Yong Luo, Xiangdong Zhang, and Jianbin Huang investigated Seward Glacier in Alaska in August 2014.